DNS record types

What is a PTR record?

A PTR record maps an IP address back to a hostname — the reverse of an A record.

Reverse DNS lives in a special zone: 4.3.2.1.in-addr.arpa for IPv4 (the octets reversed), and the thirty-two reversed nibbles under ip6.arpa for IPv6.

You cannot usually set your own PTR record. It is controlled by whoever owns the address block — your hosting provider or ISP — so it is requested rather than configured.

Example

34.216.184.93.in-addr.arpa.  3600  IN  PTR  example.com.

The mistake people make

For a mail server this is not optional. Many receivers reject or heavily penalise mail from an address with no reverse DNS, or where the PTR does not resolve back to the same address. If you run your own outbound mail server and delivery is poor, this is the first thing to check.

Check the PTR records on a real domain, with everything else that can quietly break.

Check a domain